Squamous Cell Carcinoma: Mohs Indications & Treatment
Cutaneous squamous cell carcinoma (cSCC) is the second most common skin cancer and carries a meaningful risk of local recurrence, perineural invasion, and regional/distant metastasis. Unlike BCC, high-risk SCC can be lethal. This article covers histopathologic subtypes and differentiation grading, NCCN v1.2026 risk stratification, the BWH T-staging system, indications for Mohs micrographic surgery, sentinel lymph node biopsy considerations, and emerging immunotherapy options for advanced disease.
By Dr. Yehonatan Kaplan (M.D., Fellow ACMS)·Published: 2025-03-01·Updated: 2026-03-15·Reviewed: 2026-03-07
SCCsquamous cell carcinomaMohs surgeryNCCN guidelinesBWH stagingPNIimmunosuppression
Key Takeaways
- Cutaneous SCC is the second most common skin cancer with ~1.8 million cases annually in the US and an estimated 15,000 deaths per year - unlike BCC, high-risk SCC can be lethal.
- Mohs surgery achieves 97% 5-year cure rate for primary cSCC and 90-94% for recurrent cSCC - significantly higher than standard excision.
- The BWH T-staging system (0-4 risk factors) provides superior prognostic discrimination compared to AJCC 8th edition, especially for identifying patients who benefit from SLNB.
- Perineural invasion is one of the strongest adverse prognostic factors - any caliber nerve involvement is NCCN high-risk, and large-caliber PNI (>=0.1mm) may require adjuvant radiation.
- Immunosuppressed patients (especially organ transplant recipients) have 65-250x increased SCC incidence with more aggressive behavior - Mohs is indicated for virtually all SCCs in this population.
- Cemiplimab and pembrolizumab (anti-PD-1) have transformed advanced cSCC management with ~44-47% response rates, using the high tumor mutational burden of UV-induced SCC.
Overview & Epidemiology
Cutaneous squamous cell carcinoma (cSCC) is the second most common skin cancer, accounting for approximately 20% of all nonmelanoma skin cancers. An estimated 1.8 million cases are diagnosed annually in the United States. cSCC arises from malignant transformation of epidermal keratinocytes, driven primarily by cumulative ultraviolet radiation exposure. Unlike BCC, cSCC carries a clinically significant risk of metastasis, with an overall metastatic rate of 2-5% for all comers and up to 10-30% for high-risk subgroups. Immunosuppressed patients, particularly solid organ transplant recipients, face a dramatically elevated risk. Their SCC incidence is 65-250 times higher than the general population, and their SCCs behave more aggressively with higher recurrence and metastasis rates. Other risk factors include chronic UV exposure, fair skin, HPV infection (particularly periungual and genital SCC), chronic wounds or scars (Marjolin ulcer), arsenic exposure, prior radiation therapy, and xeroderma pigmentosum. cSCC causes an estimated 15,000 deaths annually in the United States (extrapolated from Karia et al. 2013; NMSC deaths are not consistently tracked in cancer registries), making risk stratification and appropriate treatment selection critically important.
Histopathologic Subtypes & Differentiation
The histopathologic subtype and degree of differentiation are among the most important prognostic factors for cSCC. Well-differentiated SCCs show abundant keratinization, intercellular bridges, and relatively orderly maturation. They carry the lowest risk of recurrence and metastasis. Moderately differentiated tumors show intermediate features with some keratinization but increasing nuclear atypia. Poorly differentiated and undifferentiated SCCs show minimal keratinization, marked nuclear pleomorphism, and high mitotic rates. They carry the highest risk of recurrence, perineural invasion, and metastasis. Beyond differentiation grade, several histopathologic variants carry distinct prognostic implications. Desmoplastic SCC is characterized by thin cords and single tumor cells in a dense desmoplastic stroma, analogous to morpheaform BCC, with extensive subclinical extension and high recurrence rates. Acantholytic (adenoid) SCC exhibits pseudoglandular spaces due to loss of intercellular cohesion and may be confused with glandular neoplasms. Spindle cell SCC shows sarcomatoid differentiation that can be difficult to distinguish from atypical fibroxanthoma or other spindle cell neoplasms without immunohistochemistry.
| Subtype / Grade | Key Features | Risk Level | Metastatic Potential |
|---|---|---|---|
| Well-differentiated | Abundant keratinization, intercellular bridges, orderly maturation | Low | <3% |
| Moderately differentiated | Some keratinization, moderate atypia, partial maturation | Moderate | 3-5% |
| Poorly differentiated | Minimal keratinization, marked pleomorphism, high mitotic rate | High | 10-30% |
| Desmoplastic | Thin cords/single cells in dense stroma, extensive subclinical extension | High | 15-25% |
| Acantholytic (adenoid) | Pseudoglandular spaces, loss of cohesion | High | 10-15% |
| Spindle cell | Sarcomatoid differentiation, S100-/CK+, may mimic AFX | High | 10-20% |
| Verrucous | Exophytic, well-differentiated, locally destructive, pushing invasion | Low-Moderate | <2% (classic) |
Dermoscopy of SCC & Keratinocyte Neoplasms
Dermoscopy of keratinocyte skin cancer follows a progression model from actinic keratosis (AK) through intraepidermal carcinoma (IEC/Bowen disease) to invasive SCC. Unlike BCC, which has highly specific dermoscopic criteria, SCC dermoscopic features are more heterogeneous and overlap with inflammatory and other neoplastic conditions. The dermoscopic evaluation of keratinocyte neoplasms focuses primarily on vascular pattern, keratinization features, and surface architecture.
| Lesion | Dominant Vascular Pattern | Surface/Structural Features | Key Distinguishing Feature |
|---|---|---|---|
| Actinic keratosis | Red pseudonetwork (facial) | White-yellow scale, strawberry pattern | Preserved follicular openings within erythema |
| SCC in situ (Bowen) | Glomerular (coiled) vessels in clusters | Diffuse yellow opaque scales, microerosions | Clustered glomerular vessels are the hallmark |
| Invasive SCC | Hairpin + linear-irregular vessels (polymorphous) | White structureless areas, central keratin mass, ulceration | Polymorphous vascular pattern + keratinization |
| Keratoacanthoma | Hairpin vessels with white halo | Central keratotic plug/crater, white circles | Central crater with peripheral hairpin vessels |
Actinic Keratosis (AK)
Facial AK is characterized by a red pseudonetwork (erythematous background with spared hair follicle openings creating a network-like pattern), white-to-yellow surface scale, and a "strawberry pattern" (hair follicles surrounded by a white halo within a red background). The strawberry pattern is considered the most characteristic dermoscopic pattern of facial AK. Non-facial AK shows a diffuse erythematous background with white-to-yellow scale and dotted vessels.
Intraepidermal Carcinoma (Bowen Disease / SCC In Situ)
SCC in situ demonstrates a transition from the AK pattern toward more organized vascular structures. The hallmark dermoscopic features are glomerular (coiled) vessels arranged in clusters, diffuse yellow opaque scales or crusting, and surface microerosions. The glomerular vessel pattern is the most reliable dermoscopic finding for SCC in situ and corresponds histologically to dilated, tortuous capillaries within elongated dermal papillae. Brown-gray dots may be present in pigmented Bowen disease.
Invasive SCC
Invasive SCC shows a progression of dermoscopic features reflecting deeper tumor invasion and increased keratinization. Key findings include hairpin vessels (looped vessels with a keratotic halo), linear-irregular vessels (irregularly shaped, branching vessels without the organized dichotomous branching of BCC arborizing vessels), white structureless areas (corresponding to tumor-associated fibrosis and keratinization), central mass of keratin or ulceration, and targetoid hair follicles (concentric rings of white and yellow around follicular ostia). Poorly differentiated and deeply invasive SCC tends to show more polymorphous vascular patterns (mixed hairpin, linear-irregular, and dotted vessels) and white structureless areas, whereas well-differentiated SCC shows more prominent keratinization.
Keratoacanthoma
Keratoacanthoma shows dermoscopic features similar to well-differentiated invasive SCC: a central keratotic plug or crater, hairpin vessels at the periphery (often with a whitish halo), white circles (targetoid hair follicles), and a radial arrangement of vessels around the central keratin mass. Dermoscopy alone cannot reliably distinguish keratoacanthoma from well-differentiated SCC, consistent with the ongoing debate about whether keratoacanthoma represents a distinct entity or an SCC variant.
NCCN Risk Stratification (v1.2026)
The NCCN v1.2026 guidelines stratify cSCC into low-risk and high-risk categories using a thorough set of clinical and pathologic criteria. As with BCC, a tumor is classified as high-risk if any single high-risk criterion is met. The NCCN system for SCC is broader and more detailed than for BCC, reflecting the greater metastatic potential and clinical heterogeneity of SCC. High-risk features include location and size (any SCC in the H-zone, >=10mm in M-zone, >=20mm in L-zone), poorly defined clinical borders, recurrence after prior treatment, immunosuppression, prior radiation at the site, rapidly growing tumor, neurologic symptoms (pain, paresthesias, numbness), aggressive histologic subtype (poorly differentiated, desmoplastic, acantholytic, spindle cell), perineural invasion, lymphovascular invasion, and tumor depth >6mm or invasion beyond subcutaneous fat. The risk stratification directly informs the treatment algorithm and determines the intensity of workup and follow-up.
| Feature | Low Risk | High Risk |
|---|---|---|
| Location/Size | L-zone <20mm; M-zone <10mm | L-zone >=20mm; M-zone >=10mm; H-zone any size |
| Borders | Well-defined | Poorly defined |
| Primary vs. Recurrent | Primary | Recurrent |
| Immunosuppression | No | Yes |
| Prior RT at site | No | Yes |
| Rapid growth | No | Yes |
| Neurologic symptoms | None | Pain, paresthesias, numbness |
| Differentiation | Well-differentiated | Poorly/undifferentiated |
| Histologic subtype | Conventional | Desmoplastic, acantholytic, spindle cell |
| Perineural invasion | No | Yes (any caliber nerve) |
| Lymphovascular invasion | No | Yes |
| Depth / Level | Confined to dermis, <6mm | >6mm depth or beyond subcutaneous fat |
BWH T-Staging System
The Brigham and Women's Hospital (BWH) T-staging system was developed to address limitations of the AJCC 8th edition staging system for cutaneous SCC. The AJCC system has been criticized for its inability to discriminate well between risk groups, with the vast majority of cSCCs classified as T1 or T2 and poor separation of outcomes between stages. The BWH system uses four independent risk factors to stratify tumors: (1) tumor diameter >=2cm, (2) poorly differentiated histology, (3) perineural invasion of nerve >=0.1mm caliber, and (4) tumor invasion beyond subcutaneous fat. The number of risk factors present determines the T-stage. BWH T-staging has been validated in multiple studies and shows superior prognostic discrimination compared to AJCC 8th edition, particularly for identifying patients at highest risk for nodal metastasis, disease-specific death, and local recurrence. The BWH system is increasingly used alongside NCCN risk stratification to guide management decisions including SLNB consideration.
| BWH Stage | Risk Factors | Nodal Metastasis Risk | Disease-Specific Death |
|---|---|---|---|
| T1 | 0 risk factors | 0-1% | <1% |
| T2a | 1 risk factor | 3-5% | 1-2% |
| T2b | 2-3 risk factors | 15-20% | 10-15% |
| T3 | 4 risk factors | 50-60% (in select cohorts) | 30-40% (in select cohorts) |
BWH vs. AJCC 8th Edition Comparison
The AJCC 8th edition T-staging for cSCC is based on tumor diameter (T1 <2cm, T2 2-4cm, T3 >4cm or specific high-risk features) with T4 indicating bone invasion or skull base involvement. A major limitation is that 70-80% of cSCCs are classified as T1 under AJCC, providing minimal prognostic separation. The BWH system addresses this by shifting the focus from tumor size alone to a count of independent risk factors that have demonstrated prognostic value across multiple validation cohorts. BWH T2b and T3 tumors identify the patients who benefit most from intensified management, including sentinel lymph node biopsy and multidisciplinary oncologic consultation.
| Feature | AJCC 8th Edition | BWH System |
|---|---|---|
| Primary stratification | Tumor size (diameter) | Number of risk factors (0-4) |
| T1 classification | <2cm diameter | 0 risk factors |
| Prognostic discrimination | Poor (70-80% are T1) | Superior (validated in multiple cohorts) |
| SLNB guidance | Limited | T2b/T3 identifies highest-risk patients |
| Adoption | Official AJCC standard | Increasingly used in academic centers; NCCN references |
Indications for Mohs Micrographic Surgery
Mohs micrographic surgery is the preferred treatment for high-risk cSCC per NCCN v1.2026 guidelines. The indications mirror and extend beyond those for BCC, reflecting the greater biologic aggressiveness of SCC. All NCCN high-risk SCCs are candidates for Mohs, including those in the H-zone regardless of size, tumors with aggressive histologic subtypes (poorly differentiated, desmoplastic, acantholytic, spindle cell), recurrent or incompletely excised tumors, tumors with perineural invasion, and SCCs in immunosuppressed patients. The tissue conservation advantage of Mohs is particularly valuable for SCCs in cosmetically and functionally sensitive areas such as the nose, eyelids, ears, and lips. For SCCs with extensive clinical perineural invasion (symptoms or imaging-positive PNI), Mohs can be used to achieve margin control at the primary site, but adjuvant radiation therapy should be considered for the nerve pathway. Mohs achieves 5-year cure rates of 97% for primary cSCC and 90-94% for recurrent cSCC, significantly higher than standard excision.
AUC Criteria
The AAD/ACMS Appropriate Use Criteria for Mohs surgery in cSCC follow a similar framework to BCC but with heightened indications reflecting the greater aggressiveness of SCC. In Area H, Mohs is rated as appropriate for virtually all cSCCs regardless of size, differentiation, or other features. This reflects both the high recurrence risk of SCC in the central face and the critical importance of tissue conservation in this region. In Area M, Mohs is appropriate for SCCs with any high-risk feature including moderate or poor differentiation, recurrence, size greater than 10mm, immunosuppression, PNI, or prior radiation. In Area L, Mohs is appropriate for recurrent tumors, poorly differentiated SCCs, tumors with PNI, and large tumors (>20mm). The AUC system also recognizes that SCC in immunosuppressed patients warrants Mohs in any anatomic location. Proper AUC documentation should include the specific area, all tumor risk factors, and the patient immunosuppression status when applicable.
Treatment Algorithm
The NCCN v1.2026 treatment algorithm for cSCC is stratified by risk and incorporates both local and systemic management considerations. The treatment pathway differs from BCC by including mandatory consideration of nodal assessment for high-risk tumors.
Low-Risk SCC Management
Low-risk SCCs (small, well-defined, well-differentiated, primary, in M-zone or L-zone, non-immunosuppressed, no PNI) are managed with standard surgical excision using 4-6mm clinical margins. A 4mm margin achieves 95% clearance for well-defined, low-risk cSCC. Curettage and electrodesiccation (C&E) is an option for small, well-defined, low-risk SCCs on the trunk and extremities, though cure rates are lower than excision. Unlike BCC, topical therapies are generally not recommended for invasive SCC. Radiation therapy is reserved for non-surgical candidates. Close clinical follow-up with skin examination every 6-12 months is recommended.
High-Risk SCC Management
High-risk cSCC management requires a multimodal approach. Mohs micrographic surgery is the preferred primary treatment, providing the highest cure rate with tissue conservation. When Mohs is unavailable, wide excision with 6-10mm margins and CCPDMA is recommended. For tumors with extensive perineural invasion (clinical PNI or large-caliber histologic PNI involving nerves >=0.1mm), adjuvant radiation therapy to the primary site and nerve pathway should be considered. High-risk SCCs should prompt assessment of the regional lymph node basin by clinical examination and imaging (ultrasound or CT) when indicated. Multidisciplinary tumor board discussion is recommended for BWH T2b/T3 tumors, tumors with clinical PNI, lymphovascular invasion, or regional nodal involvement.
Sentinel Lymph Node Biopsy
Sentinel lymph node biopsy (SLNB) for cSCC remains an evolving area of practice. Unlike melanoma, where SLNB is well-established with clear survival benefit data, the role of SLNB in cSCC is less definitively established but increasingly supported by accumulating evidence. NCCN v1.2026 states that SLNB may be considered for high-risk cSCC with features suggesting elevated metastatic risk. The strongest evidence for SLNB benefit exists for BWH T2b and T3 tumors, which carry nodal metastasis rates of 15-20% and 50-60% respectively (in select validation cohorts; sample sizes for T3 are small). Additional features that should prompt SLNB consideration include extensive perineural invasion (large-caliber nerve involvement), lymphovascular invasion, poorly differentiated or undifferentiated histology, tumor depth >6mm, invasion beyond subcutaneous fat, and immunosuppression with aggressive tumor features. When SLNB is positive, completion lymph node dissection or adjuvant radiation to the nodal basin should be discussed, and systemic therapy may be considered. SLNB should ideally be performed concurrently with the definitive surgical procedure (Mohs or wide excision) to avoid disrupting lymphatic drainage patterns.
Advanced & Metastatic SCC
Locally advanced and metastatic cSCC has been transformed by the approval of immune checkpoint inhibitors. Cemiplimab (Libtayo), an anti-PD-1 monoclonal antibody, was the first FDA-approved systemic therapy for advanced cSCC, demonstrating an overall response rate of approximately 44% in locally advanced disease and 47% in metastatic disease (EMPOWER-CSCC-1 trial), with durable complete responses in a meaningful subset of patients. Pembrolizumab (Keytruda) subsequently received FDA approval for recurrent or metastatic cSCC, demonstrating similar efficacy. The high mutational burden of UV-induced cSCC (one of the highest of any solid tumor) likely contributes to the favorable response to immunotherapy, as neoantigen-rich tumors tend to elicit stronger immune responses. For patients who are not candidates for immunotherapy (autoimmune disease, organ transplant recipients requiring immunosuppression), radiation therapy remains an important treatment option. Combination strategies (immunotherapy + radiation, immunotherapy + targeted therapy) are under active investigation. NCCN v1.2026 recommends multidisciplinary evaluation for all patients with regionally advanced or metastatic cSCC.
Prognosis & Follow-up
The prognosis for cSCC depends heavily on the risk stratification at diagnosis. Low-risk cSCC treated with appropriate surgical margins carries an excellent prognosis with recurrence rates under 5%. High-risk cSCC, particularly BWH T2b/T3, has significant rates of local recurrence (10-20%), regional metastasis (15-60%), and disease-specific death (10-40%). Mohs micrographic surgery achieves 5-year cure rates of 97% for primary cSCC and 90-94% for recurrent cSCC. NCCN v1.2026 recommends follow-up every 3-6 months for the first 2 years, then every 6-12 months for 3 more years, then annually. High-risk patients (immunosuppressed, multiple high-risk tumors, positive SLNB) warrant more intensive surveillance. Follow-up should include full skin examination, palpation of draining lymph node basins, and imaging (CT, MRI, or PET/CT) when clinically indicated. Patient education regarding sun protection, self-examination, and recognition of new lesions is essential. The 3-year risk of a subsequent SCC after a first cSCC is approximately 18%, and patients with SCC also have elevated risk of BCC and melanoma.
| BWH Stage | 5-Year Local Recurrence | 5-Year Nodal Metastasis | 5-Year Disease-Specific Death |
|---|---|---|---|
| T1 (0 factors) | <3% | <1% | <1% |
| T2a (1 factor) | 5-10% | 3-5% | 1-2% |
| T2b (2-3 factors) | 15-20% | 15-20% | 10-15% |
| T3 (4 factors) | 30-40% | 50-60%* | 30-40%* |
Frequently Asked Questions
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About This Article
Author: Dr. Yehonatan Kaplan, M.D., Fellow ACMS
Last Medical Review:
Audience: Dermatologic Surgeons
Clinic: Kaplan Clinic · DermUnbound Research Program